Methoxy and bromo scans on N-(5-methoxyphenyl) methoxybenzenesulphonamides reveal potent cytotoxic compounds, especially against the human breast adenocarcinoma MCF7 cell line

Thirty seven N-(5-methoxyphenyl)-4-methoxybenzenesulphonamide with methoxy or/and bromo substitutions (series 1-4) and with different substituents on the sulphonamide nitrogen have been synthesised. 21 showed sub-micromolar cytotoxicity against HeLa and HT-29 human tumour cell lines, and were particularly effective against MCF7. The most potent series has 2,5-dimethoxyanilines, especially the 4-brominated compounds 23–25. The active compounds inhibit microtubular protein polymerisation at micromolar concentrations, thus pointing at tubulin as the target. Co-treatment with the MDR inhibitor verapamil suggests that they are not MDR substrates. Compound 25 showed nanomolar antiproliferative potency. It severely disrupts the microtubule network in cells and arrests cells at the G₂/M cell-cycle phase, thus confirming tubulin targeting. 25 triggered apoptotic cell death, and induced autophagy. Docking studies suggest binding in a distinct way to the colchicine site. These compounds are promising new antitumor agents acting on tubulin.

Exploring Diverse-Ring Analogues on Combretastatin A4 (CA-4) Olefin as Microtubule-Targeting Agents

Combretastatin-4 (CA-4) as a tubulin polymerization inhibitor draws extensive attentions. However, due to its weak stability of cis-olefin and poor metabolic stability, structure modifications on cis-configuration are being performed. In this work, we constructed a series of novel CA-4 analogues with linkers on olefin containing diphenylethanone, cis-locked dihydrofuran, α-substituted diphenylethanone, cyclobutane and cyclohexane on its cis-olefin. Cytotoxic activity of all analogues was measured by an SRB assay. Among them, compound 6b, a by-product in the preparation of diphenylethanone analogues, was found to be the most potent cytotoxic agents against HepG2 cells with IC₅₀ values of less than 0.5 μM. The two isomers of 6b induced cellular apoptosis tested by Annexin V-FITC and propidium iodide (PI) double staining, arrested cells in the G2/M phase by PI staining analysis, and disrupted microtubule network by immunohistochemistry study in HepG2 cells. Moreover, 6b-(E) displayed a dose-dependent inhibition effect for tubulin assembly in in vitro tubulin polymerization assay. In addition, molecular docking studies showed that two isomers of 6b could bind efficiently at colchicine binding site of tubulin similar to CA-4.

Constructing novel dihydrofuran and dihydroisoxazole analogues of isocombretastatin-4 as tubulin polymerization inhibitors through [3+2] reactions

[3+2] reactions play a key role in constructing various pharmaceutical moleculars. In this study, using Mn(OAc)₃ mediated and 1,3-dipolar [3+2] cyclization reactions, 38 novel dihydrofuran and dihydroisoxazole analogues of isoCA-4 were synthesized as inhibitors of tubulin polymerization. Among them, compound 6g was found to be the most potent cytotoxic agents against PC-3 cells with IC₅₀ value of 0.47μM, and compound 5p exhibted highest activity on HeLa cells with IC₅₀ vaule of 2.32µM. Tubulin polymerization assay revealed that 6g was a dose-dependent and effective inhibitor of tubulin assembly. Immunohistochemistry studies and cell cycle distribution analysis indicated that 6g severely disrupted microtubule network and significantly arrested most cells in the G2/M phase of the cell cycle in PC-3 cells. In addition, molecular docking studies showed that two chiral isomers of 6g can bind efficiently and similarly at colchicine binding site of tubulin.